Oven for shrinking wrappers



Nov. 10, 1964 D. FORMAN ETAL OVEN FOR sHRzNxING wRAPPERs 2 Sheets-Sheet l Filed Feb. 14, 1962 M u n e .k 2 l ...m y. F l 5 2//2 2 2 2 4 9 4 l G l .r l 2 4,. M' 2 2 d INVENTORJ DAVID FORMAN Aumu HAROLD M. F O RM A N ggIIIIIIIIIIIFIIII||||||||IIIIIIIIIIIIIIII` m l ATTORNEY BYW;

Nov. l0, 1964 D. FORMAN ETAL AOVEN FOR SHRINKINGWRAPPERS 2 Sheets-Sheet 2 Filed Feb- 14, 1962 FIG. 6.

INVENTORS DAVID FORMAN HAROLD M. FORMAN BYQZWL FIG. 7.

ATTORNEY United States Patent O 3,156,8i2 OVEN EUR Sl-iRllslKlNtC- WRAPPERS David Forman and Harold M. Forman, both of Philadelphia, Pa., assignors to Formation, lne., Philadelphia, Pa., a corporation of Pennsylvania Filed Feb. 14, 1962, Ser. No. 173,209 Claims. (Cl. Zig-SSS) This invention relates to the art of packaging and it is more particularly concerned with the application of heat shrinkable wrappers to packages of various articles, especially those of irregular shape, including food products.

The use of heat shrinkable wrappers is well known in the packaging art and generally involves the application of a relatively loose envelope about the package. The envelope comprises one or the various heat shrinlrable sheets available commercially and after it is placed about the package or products to be held together, it is passed through a furnace or oven to shrink the sheet tightly about the pacicage or products enveloped thereby. This results not only in a package which has a pleasing appearance, provided the shrinking is properly performed, but one in which the various elements or the package are held together', such as in the case of a group of potatoes, balls, hardware, etc.

ln practicing the art, it is important to provide a nal product at a minimum cost and one which is attractive to the consumer. This requires the use of an oven for shrinking the sheet that is highly ecient and also one which applies overall uniform heat to each package as it passes through the oven.

Accordingly, it is an object of the invention to apply heat to a package eneveloped with a heat shrinlrable sheet that will result in a uniform shrinking of the sheet thereabout.

It is another object of the invention to apply the heat to the package economically and efficiently.

A further object of the invention is the provision of an oven for the purpose indicated which can be maintained at its operating temperature irrespective of whether it is in 'operation or to what extent.

A still further object of the invention is the provision of such an oven which minimizes or obviates diherential shrinkage and wrinkling of the envelope sheets.

A still further object of the invention is to provide appratus which is compact, easy to construct and use, and which can be fabricated in various sizes as may be required.

A still further object and feature of the invention is the provision of an oven of the type mentioned in which the temperature control is effected by means of air drawn into the oven and circulated through a control panel between the oven and constantly energized heating units.

These and still further objects, advantages, and features of the invention will appear more fully from the following description considered together with the accompanying drawing.

In the drawing:

FIG. 1 is a rear elevational view of an embodiment of the invention.

FIG. 2 is a side elevational view of the embodiment.

FIG. 3 is a longitudinal sectional View along the line 3 3 of FIG. l.

FIG. 4 is a cross-sectional view along the line i-d of FIG. 3.

3,155,3l2 Patented Nov. 10, 1964 PIG. 5 is a plan sectional view along the line 5-5 of FG. 3.

FIG. 6 is a plan sectional view along the line 6 6 of FlG. 3.

FIG. 7 is a fragmentary View showing the damper operculum in closed position.

FiG. 8 is a view similar to FIG. 7 showing the damper operculurn in the open position.

Referring with more particularity to the drawing in which like numerals designate like parts throughout the various views, the embodiment illustrated comprises an elongated table l1 supported on legs 12 or by any other suitable means.

At the front and rear of the top 13 of the table there are mounted rollers 14 and l5, respectively, for an endless conveyor belt 16, the upper flight of which overlies the top 13.

One of the rollers, say roller l5, is power driven by an electric motor 17 attached to the table through sprockets lil and i9 and sprocket chain 2t). The surfaces of the rollers are preferably iluted or corrugated to resist slippage of the belt 16 thereon.

The belt conveyor is associated with an electric oven or furnace El. supported on the table 11, and which comprises a top panel 22, side panels 23, 24 and end panel sections 25, 26 connected to the top and side panels forming together a rigid enclosure. Flexible curtain members 27, 2S are secured to the sections 25, 26, respectively, and cover the openings below as the entrance and exit of the oven between which the packages are moved by the belt conveyor. These curtains may be of any suitable heat resistance material, including any of the conventional plastic sheet materials, treated fabrics, etc.

Attached to the top panel 22 on the interior of the enclosure and to either side of the center thereof, are banks or electric heating units 29, 36 of the Calrod type where the electrical heating elements are embedded and shielded from the ambient atmosphere.

Below the heating units 29, 3l) there is disposed the circulation control panel 31. It is held in spaced relation relative to the top panel 22 by cleats 32, 33 and secured thereto by bolts 34, 35, respectively.

The sides of the circulation control panel 31 are provided with median cut out sections 36 and 37 and with a central opening 3S between said cut out sections. In the pocket or space 39 between the circulation control panel 31 and the top panel 22, there is disposed adjacent the opening 3% a rotary fan di? on the shaft 41 of an electric motor 42. The motor is mounted on the top panel 22 or at any other convenient place.

Alongside the motor 42., an opening d3 is provided in the top panel 22 for the lid or operculurn ld of a damper valve. A stem l5 is secured to, projects upwardly from the operculum and is attached to the vertically movable armature lo of a solenoid 47.

The bottom side of the opening 43 is covered with a screen t8 to catch foreign objects which may enter the opening under the iniluence of air drawn in by the fan.

The solenoid 47 is an integral part of an electrical control box 49 having conventional electrical devices, including relays, transformers, resistors, fuses, etc., through which electricaly power is fed from a supply line E@ and distributed to the conveyor motor 17, the fan motor 4Z, the solenoid d'7, the heating units 29, 30, etc.

A thermostat Si is mounted on the inside of the oven by means `of a bracket 52 and it is electrically connected to the solenoid d'7 by conventional means (not shown) to actuate it within the selected temperature limits.

In operation, packages 'S3 enveloped in heat shrinkable films lor sheets, such as Plioiilm, etc., is placed on the belt conveyor in front of the entrance curtain 27 and is carried by the conveyor into the oven. The temperature of the oven is preconditioned by energizing the electrical heating units 29, 3? and turning on the fan motor 42, both of which remain in this active condition throughout the operation.

The circulation of the air under the influence of the fan 4d and the circulation control panel 3l is between the central opening 38 and the median side openings 36 and 37, respectively, transversely of the direction of travel of the packages through the oven, whereby a uniform temperature is maintained across the path 'of travel of the packages. This hasrthe effect of preventing or minimizing differential shrinkage, wrinkles, and distortion of the iilm, because the entire envelope at any given moment is at once subjected to substantially the same temperature. Such distortion is particularly undesirable where the iilm contains printed matter.

In accordance with the present invention, the heating units 29, Sii are always energized while the oven is in operation. Temperature control is effected by admitting air from the exterior through the damper opening 43. This has man-y advantages and it is a distinct feature of the invention. Alt permits the use of encased heating elements in the heating units which are long lasting because they are shielded from the ambient air and hence are not exposed to oxidation. Also, the temperature control is` more rapid, sensitive and eicient than it is in cases where the control is effected by the turning on and oit"y of the electrical heating elements.

This method of controlling the oven .temperature also provides a constant temperature regardless of whether the packages are being passed through the oven. Accordingly, preconditioning to exact requirements is possible before the oven is placed in operation. Also the temperature remains uniform under conditions of slowdown or stoppage as may occur on occasions during a run so that the oven is always in condition to resume normal operations without a time lag. This is not usually possible in the case of ovens where a change in temperature is effected only by turning the heating elements on or of, because a definite time lag is required for the heat transfer to take effect by radiation. In the case of a required reduction in temperature, for example, the radiation must take place through the walls of the oven. If the oven walls have been made of or include heat insulating material to conserve heat losses, considerable time will be lost until the correct temperature is obtained.

Having thus described our invention, we claim:

1. An oven for shrinking heat shrinkable envelopes on packages comprising members forming an enclosure having a top panel, side panels, end panels and-an open bottom,` said end panels having entrance and exit openings, respectively, deiining the terminals of the path of travel of the packages through the enclosure, said open bottom being adapted to receive a mechanical conveyor in the space between the openings in said end panels; an air circulation control panel above the path of travel,V below and in spaced relation to the top panel; said control panel having side air exhaust openings at a median zone on either side of the path of travel for the movement of air to the oven from the space between the control panel and the said top panel; said control panel having also a central air intake opening in the median zone between said side openings; air circulation means adjacent said air intake opening and electrical heating units in the space between the top panel and the` control panel in the path of air travel between the intake opening and the side openings; a vfresh air damper between thecexterior of the enclosure and the space between said top and control panels; and means responsive to temperature changes within the enclosure for actuating said damper to control the flow of primary air from the exterior of the enclosure to the interior space between said top and control panels.

Z. An oven for shrinking heat shrinkable envelopes on packages comprising members forming an enclosure having a top panel, side panels, end panels and an open bottom, said end panels having entrance and exit openings, respectively, deining rthe terminals of the path of travel of the packages through the enclosure, said open bottom being adapted to receive a mechanical conveyor in the space between the openings in said end panels, an air circulation control panel between the top panel and the path of travel, means supporting the cont-rol panel in spaced relation to the top panel; said control panel having side air exhaust openings at a median zone on either side Y of the path of travel; said control panel having also a central air intake opening in the median Zone betweenV said side openings; air circulation means adjacent said inlet opening adapted to draw air into the space between the control panel and the top panel from the oven and return it to the oven through said exhaust openings and electrical heating units in the space between said top and control panels along the paths of travel of air between the intake opening and the exhaust openings; a fresh air damper between the exterior of the enclosure and the space between said top and control panels; and means responsiveto temperature changes within the enclosure for actuating said damper to control the ow of primary air from the exterior of the enclosure to the interior space between said top and control panels.

3. An oven for shrinking heat shrinkable envelopes on packages comprising members forming an enclosure with entrance and exit openings, said openings being separate each from the other defining the terminals of the path of travel of the packages through the enclosure; a rnechanical conveyor along the path of travel for transporting the packages between said entrance and exit openings; one of said members comprising a top panel; an air circulation control panel between the top panel and the path of travel; means supporting the control panel in spaced relation to thetop panel; said control panel having median air exhaust openings on either side of the path of travel; said control panel having also an air intake opening between said median exhaust openings; air circulation means adjacent said intake opening and electrical Y heating units in the space between said panels in the path of travel between the intake opening and the exhaust openings; a fresh air damper between the exterior of the enclosure and the space between said panels;rand means responsive to temperature changes within the enclosure for actuating said damper.

4. An oven as deiined by claim l in which the heating units comprise embedded electrical resistance elements Y shielded from contact with the ernbient atmosphere.

5. An oven comprising a box-like structure having entrance and exit openings separate each from the other; means for conveying articles to be treated between said openings; means forming an air pocket on the interior of the oven above the path of travel of the Varticles therethrough; said last mentioned means including an air circulation control panel; said panel having median air exhaust openings therein at its sides oneither side of the path of travel of the articles through the oven and having also an air intake opening between said medianV open- Y ings; air circulation means adjacent the air intake opening and electrical heating units in said pocket in the paths of air travel between theair intake opening and the air exhaust openings; a damper for selectively admitting fresh air from the exterior of the structure to said pocket;

and means responsive to temperature changescwithin the oven for actuating said damper.

(References on following page) References Cited in the 111e of this patent UNITED STATES PATENTS Fuller Dec. 14, 1920 Ellis sept. 25, 1923 Woodson Nov. 11, 1924 Shroyer Dec. 25, 1928 Marsh etal Oct. 14, 1930 Fulmer Jan. 6, 1931 Martn Nov. 1, 1932 Belcher Mar. 21, 1939 6 Cramer Apr. 15, 1941 Bates May 12, 1942 Buckholdt Sept. 22, 1942 Merrill Oct. 15, 1946 Wood Feb. 27, 1951 Foulder et a1 Aug. 12, 1952 Rollins Apr. 7, 1959 Dreyfus et a1 'Septl 22, 1959 Payton et a1 Sept. 29, 1959 Murphy Mar. 28, 1961 Moore Aug. 6, 1963 

1. AN OVEN FOR SHRINKING HEAT SHRINKABLE ENVELOPES ON PACKAGES COMPRISING MEMBERS FORMING AN ENCLOSURE HAVING A TOP PANEL, SIDE PANELS, END PANELS AND AN OPEN BOTTOM, SAID END PANELS HAVING ENTRANCE AND EXIT OPENINGS, RESPECTIVELY, DEFINING THE TERMINALS OF THE PATH OF TRAVEL OF THE PACKAGES THROUGH THE ENCLOSURE, SAID OPEN BOTTOM BEING ADAPTED TO RECEIVE A MECHANICAL CONVEYOR IN THE SPACE BETWEEN THE OPENINGS IN SAID END PANELS; AN AIR CIRCULATION CONTROL PANEL ABOVE THE PATH OF TRAVEL, BELOW AND IN SPACED RELATION TO THE TOP PANEL; SAID CONTROL PANEL HAVING SIDE AIR EXHAUST OPENINGS AT A MEDIAN ZONE ON EITHER SIDE OF THE PATH OF TRAVEL FOR THE MOVEMENT OF AIR TO THE OVEN FROM THE SPACE BETWEEN THE CONTROL PANEL AND THE SAID TOP PANEL; SAID CONTROL PANEL HAVING ALSO A CENTRAL AIR INTAKE OPENING IN THE MEDIAN ZONE BETWEEN SAID SIDE OPENINGS; AIR CIRCULATION MEANS ADJACENT SAID AIR INTAKE OPENING AND ELECTRICAL HEATING UNITS IN THE SPACE BETWEEN THE TOP PANEL AND THE CONTROL PANEL IN THE PATH OF AIR TRAVEL BETWEEN THE INTAKE OPENING AND THE SIDE OPENINGS; A FRESH AIR DAMPER BETWEEN THE EXTERIOR OF THE ENCLOSURE AND THE SPACE BETWEEN SAID TOP AND CONTROL PANELS; AND MEANS RESPONSIVE TO TEMPERATURE CHANGES WITHIN THE ENCLOSURE FOR ACTUATING SAID DAMPER TO CONTROL THE FLOW OF PRIMARY AIR FROM THE EXTERIOR OF THE ENCLOSURE TO THE INTERIOR SPACE BETWEEN SAID TOP AND CONTROL PANELS. 